1. Field of the Invention
The present invention relates to a pulverized coal combustion burner to be applied to a pulverized coal firing boiler, a chemical industrial furnace, etc. for public power utilities and other industries.
2. Description of the Prior Art
FIG. 11 is a longitudinal sectional view showing an example of a cylinder type pulverized coal burner in the prior art which is a basis of the present invention. FIG. 12 is a front view of the same, and FIG. 13 is a transverse sectional view taken on line VIII--VIII of FIG. 11. In this burner, there is provided an oil gun (01) for stabilizing combustion at the axial center portion of the burner, and an oil primary air flow path (13) surrounding the oil gun (01) partitioned at its outer circumference by an oil primary air pipe (02). A pulverized coal and primary air mixture flow path (14) is on the outer side of the oil primary air flow path (13) partitioned at its outer circumference by a primary air pipe (03). A secondary air flow path (15) is further on the outer side of the pulverized coal and primary air mixture flow path (14), partitioned at its outer circumference by a secondary air pipe (04), and a tertiary air flow path (16), further, is on the outer side of the secondary air pipe (04), partitioned at its outer circumference by an outer cylinder.
At a terminal end portion of the oil primary air flow path (13), a swirl vane (05) is provided for maintaining stable flames of heavy oil. The oil primary air is supplied at a ratio of 5% to 10% of the entire air amount as auxiliary air at the time of heavy oil firing or combustion stabilizing.
Secondary air and tertiary air for main combustion are divided into the secondary air and the tertiary air by an air wind box (09). The secondary air is given the necessary swirl forces by a secondary swirl vane (07) and is supplied into a furnace through the secondary air flow path (15) and a secondary air nozzle (18). Likewise, the tertiary air also is given necessary swirl forces by a tertiary air swirl vane (08) and is supplied into the furnace through the tertiary air flow path (16) and a tertiary air nozzle (19).
On the other hand, as shown in FIG. 13, pulverized coal as a main fuel is supplied into the burner together with the primary air for carrying via a pulverized coal supply pipe (11) connected perpendicularly to the primary air pipe (03), and is carried further into the furnace through the mixture flow path (14) and a pulverized coal nozzle (17). The pulverized coal jetted from the pulverized coal nozzle (17) is ignited and burns as it diffuses and mixes with the secondary air and the tertiary air. Complete combustion takes place with the air from an after-air port (not shown) provided downstream of the furnace.
Incidentally, at a terminal end portion of the secondary air nozzle (18) which corresponds to the outer circumference of the primary air and pulverized coal mixture flow path (14), there is provided a flame stabilizing plate (06).
In the axially symmetrical cylinder type burner in the prior art, there is the following shortcoming.
As pulverized coal supplied into the burner flows in perpendicularly to the axis of the primary air pipe (03), bias flows occur in the pulverized coal and primary air mixture flow path (14), and the pulverized coal density distribution in the circumferential direction at the outlet portion of the pulverized coal nozzle (17) becomes extremely non-uniform. Accompanying this, the distance between the burner and the point of ignition of the pulverized coal becomes non-uniform in the circumferential direction. That is, in the area where the pulverized coal density is high, the ignition point is near, and in the area where it is low, the ignition point becomes far. If the ignition point becomes non-uniform, there is a fear of the burner being damaged by heat in the area where the ignition point is near. Further, in the area where the ignition point is far, as the secondary air has already partially diffused, the air ratio at the ignition point becomes high and an oxidation flame is generated. Thus an increased amount of NO.sub.x is generated.
Following is a description of a burner in the prior art shown in FIG. 14 and FIG. 15.
FIG. 14 is a longitudinal sectional view showing an example of a coal firing cylinder type burner in the prior art, and FIG. 15 is a transverse sectional view taken on line V--V of FIG. 14. In these figures, each numeral designates a respective component and part as follows: (201) a burner wind box, (202) a pulverized coal and primary air mixture cylinder, (203) a flame stabilizing plate, (204) a secondary air cylinder, (205) a tertiary air cylinder, (206) an oil burner gun guide pipe, (207) an oil burner gun, (208) a pulverized coal dense/thin separator, (209) a secondary air amount adjusting damper, (210) a secondary air swirl vane, (211) a tertiary air swirl vane, (212) a pulverized coal mixture throwing pipe, (213) a burner front wall, (214) a pulverized coal mixture compartment, (215) a secondary air compartment, (216) a tertiary air compartment, (217) a secondary air amount adjusting damper operation lever, (218) a secondary air swirl vane operation lever, (219) a tertiary air swirl vane operation lever, (220) seal air, (221) pulverized coal mixture, (222) secondary air, (223) tertiary air, (224) liquid fuel and (225) a boiler furnace.
Combustion air supplied from air blowing equipment (not shown) is divided, while it is flowing, into the secondary air (222) and the tertiary air (223) within the burner wind box (201).
The secondary air (222) is adjusted to the necessary amount by the-secondary air amount adjusting damper (209) operated by an operation lever (217) and is supplied into the secondary air compartment (215) within the secondary air cylinder (204) via the secondary air swirl vane (210) operated by an operation lever (218) and then is blown into the boiler furnace (225). The remaining combustion air is supplied as the tertiary air (223) into the tertiary air compartment (216) within the tertiary air cylinder (205) via the tertiary air swirl vane (211) and then is blown into the boiler furnace (225).
Coal as a fuel is pulverized by coal pulverization equipment (not shown), is mixed with the primary air and is supplied as the pulverized coal mixture (221) to be blown into the pulverized coal mixture compartment (214) within the pulverized coal mixture cylinder (202) from the pulverized coal mixture throwing pipe (212). At the terminal end of the pulverized coal mixture cylinder (202), the flame stabilizing plate (203) is provided and, inside thereof, the oil burner gun guide pipe (206) passing through the pulverized coal mixture cylinder (202) is provided. On the outer circumference of the oil burner gun guide pipe (206), the cylindrical pulverized coal dense/thin separator (208), the front part and the rear part of which are reduced, is provided so as to be positioned near the outlet of the pulverized coal mixture compartment (214).
Within the oil burner gun guide pipe (206), there is provided the oil burner gun (207) for atomized combustion of the liquid fuel (224). Combustion of the liquid fuel (224) by the oil burner gun (207) is made for the purpose of raising the temperature within the boiler furnace (225) before pulverized coal combustion is commenced. Within the oil burner gun guide pipe (206), the seal air (220) is continuously supplied from air blowing equipment (not shown) so that the oil burner gun guide pipe (206) may not be blocked by the pulverized coal after the pulverized coal combustion is commenced.
The pulverized coal mixture (221) blown into the pulverized coal mixture compartment (214) is accelerated while it passes around the outer circumference of the pulverized coal dense/thin separator (208), and at the outlet portion of the pulverized coal mixture compartment (214) it suddenly expands and is decelerated. At this time, the pulverized coal within the pulverized coal mixture (221) flows, for the most part, biassed by the inertia force to the outer circumferential side, or along the inner wall surface side of the pulverized coal mixture cylinder (202). On the center portion side of the outlet of the pulverized coal mixture compartment (214), there flows the primary air within the pulverized coal mixture (221) and a small amount of the pulverized coal of fine particles mixed therewith. Accordingly, the jet flow of the pulverized coal mixture (221) blown into the boiler furnace (225) has a density distribution wherein the pulverized coal density is high on the surface (outer side) and is low on the inner side.
The flame stabilizing plate (203) provided at the terminal end of the pulverized coal mixture cylinder (202) generates swirl flows of the secondary air (222) flowing on the outer circumference of the pulverized coal mixture cylinder (202) on the back side surface of the flame stabilizing plate (203). Thus the pulverized coal on the surface (outer side) of the jet flow of the pulverized coal mixture (221) is taken therein and ignited, and the pulverized coal flame at the ignition portion is stabilized.
The pulverized coal mixture (221) blown into the boiler furnace (225) from the pulverized coal mixture cylinder (202) is ignited by an ignition source (not shown), while at around the jet portion the pulverized coal mixture (221) is ignited on the surface side of the jet flow of the pulverized coal mixture (221). As it proceeds downstream of the jet flow of the pulverized coal mixture (221), ignition proceeds in the direction of the inner side, and thus pulverized coal flames are generated. FIG. 16 is a schematic drawing showing a model of a pulverized coal flame. The nearer the ignition point is to the jet portion of the pulverized coal mixture (221), the more the pulverized coal flame tends to stabilize. At the ignition point of the pulverized coal flame, as shown in FIG. 16, the surface of the jet flow of the pulverized coal mixture (221) is heated by an ignition source. Thereby a volatile content is generated and ignited. Accordingly, if the pulverized coal density on the surface side of the jet flow is high near the jet portion of the pulverized coal mixture (221), the ignition point of the pulverized coal flame comes nearer to the jet portion, and stable pulverized coal flames are generated. The pulverized coal flames so generated continue combustion by the secondary air (222) and the tertiary air (223) blown from the circumference thereof.
In the above described coal firing cylinder type burner in the prior art shown in FIG. 14 and FIG. 15, there are shortcomings to be solved as follows.
While the pulverized coal density distribution adjustment of the jet flow of the pulverized coal mixture (221) at the outlet of the pulverized coal mixture compartment (214) is made by the pulverized coal dense/thin separator (208), the pulverized coal density on the surface side of the jet flow does not become high enough. Thus in a combustion of low volatile content coals in which the fuel ratio (ratio of solid carbon content and volatile content) is high, the ignition point of the pulverized coal flame is moved far from the outlet of the pulverized coal mixture compartment (214). Thus the ignition stability of the flame is not good enough.
Further, if the combustion amount within the boiler furnace (225) is decreased, the pulverized coal density of the pulverized coal mixture (221) supplied from coal pulverizing equipment becomes lower and the ignition stability of the pulverized coal flame in low load combustion becomes worse.
Following is a description of a burner in the prior art shown in FIG. 17.
FIG. 17 is a schematic longitudinal sectional view of a main part of a pulverized coal burner in the prior art. An outer circumferential cylinder (307) is on the inner side of a furnace wall port (309) via a tertiary air jet port (308). A burner body (3011) is at the center on the inner side of the outer circumferential cylinder (307) via a secondary air jet port (306). Pulverized coal and primary air are supplied from the burner body (3011).
A duct damper (not shown) is provided at an inlet on the left side of the figure, and the air amount is increased or decreased unitarily, not by each of the primary to the tertiary flow paths.
The right side of FIG. 17 is a conceptual drawing of combustion, which shows that the combustion proceeds downstream with two stages. A reduction atmosphere stage has the air ratio less than 1, and an oxidation atmosphere stage has the air ratio more than 1. That is, the pulverized coal first has volatile content combustion in the reduction atmosphere and generates NO.sub.x, and then has combustion to convert to N.sub.2. or an oxidation combustion.
Recently, as is known, since low NO.sub.x is required for every kind of exhaust gasses, in the above-mentioned combustion also, in order to immediately convert the NO.sub.x generated in the reduction atmosphere to N.sub.2 air (oxygen in fact) could be supplied quickly within the range where the temperature does not decrease. But, there is a problem in that if, for example, the primary air amount supplied is too much of the ratio of cooling heat to combustion heat becomes too high so that the volatile content combustion does not develop. And even if the primary air amount is appropriately suppressed and the secondary and tertiary air are increased, due to the air flow line made by the terminal end (the right end of the figure) of the burner body (301') and the outer circumferential cylinder (307) being open like a funnel, as shown in figure, the air is not able to mix well into the combustion area unless it comes comparatively downstream. Needless to mention, the funnel-like opening at the terminal end of the burner body (301') and the outer circumferential cylinder (307) is indispensable for air to be uniformly mixed into so-called combustion flames of a generation gas (NO.sub.x etc.), air, etc. within the combustion area, which makes a sudden expansion by combustion, and that the current velocity of frames is appropriately suppressed so as to secure enough heat transmission to be the furnace wall pipes, etc.
The NO.sub.x generation amount in relation to the reduction atmosphere temperature taken at the portion when the pulverized coal finishes combustion after the reduction atmosphere and the oxidation or on the extreme right side of FIG. 17, is shown in FIG. 18. This figure shows that the higher the reduction atmosphere temperature, the lesser the NO.sub.x amount.
FIG. 19 is a diagram showing the relation between the secondary air amount and the coal volatile amount in the example shown in FIG. 18.
In the above-described pulverized coal combustion burner in the prior art shown in FIG. 17, there are such shortcomings to be solved as follows.
In this pulverized coal combustion burner in the prior art, the jet ports of the primary air carrying the pulverized coal and of the secondary and tertiary air are fixed, and the air amount cannot be adjusted to the kind of coal at the jet ports. Accordingly, the adjustment of the air amount is made by the usual duct damper provided at the inlet being adjusted.
A low NO.sub.x combustion by the pulverized coal combustion burner depends on how quickly the coal volatile content combustion is made at the reduction are immediately after the jet ports, and how quickly the generated NO.sub.x is converted to N.sub.2 while the temperature does not decrease downstream. But, as the volatile content varies according to the kind of coal, and many kinds of coal are used in a power station, there is a problem in that pulverized coal combustion burner in the prior art has funnel-like openings fixed so that the mixing area of the secondary air comes downstream and a low NO.sub.x combustion is not well attuned to the kind of coal.